Radio terminal unit, radio communication system and communication control method

ABSTRACT

A radio terminal unit and a radio communication system, enabling power savings, the improvement of the quality of real-time communication such as voice communication, and the reduction of transmission delays which often occur when a plurality of radio terminal units are connected to one radio base station. A radio terminal unit comprises an operation mode of communication application determination unit for determining operation mode of one or more communication which is operated at the radio terminal unit, a control packet changing unit for changing a timing of transmission of the control packet according to the operation mode of one or more communication applications determined by the operation mode of communication application determination unit, and a communication control section for sending the control packet according to the timing of transmission changed by the control packet changing unit after the transmission of data from the application.

FIELD OF THE INVENTION

The present invention relates to a radio terminal unit and a radiocommunication system including the same, and more particularly, to aradio terminal unit, a radio communication system and a communicationcontrol method, in which a radio base station connected to each radioterminal unit by radio as a transmission medium is connected to a LAN(Local Area Network) or a WAN (Wide Area Network).

BACKGROUND OF THE INVENTION

In a conventional wireless LAN system making use of radio as atransmission medium, for example, in a radio communication systemdisclosed in Japanese Patent Application laid open No. HEI9-162798(FIGS. 14 and 20), power-saving operation in a radio terminal unit iscarried out by intermittently receiving beacons from a radio basestation. Besides, it is required to receive at least a beacon having adelivery traffic indication map (DTIM) in order to obtain amulticast/broadcast packet.

That is, when a radio terminal unit enters power-saving mode, the radioterminal unit obtains a beacon transmitted from a radio base station.Having extracting respective information elements included in thebeacon, the radio terminal unit carries out intermittent receivingoperation based on beacon interval information included within thebeacon and an interval between the transmission of beacons each having adelivery traffic indication map (hereinafter referred to as “DTIM”).

When operating in power-saving mode, the radio terminal unit informs theradio base station of its operation using a frame control field. Theradio base station buffers packets addressed to the radio terminal unitoperating in power-saving mode in a memory within the radio basestation, and informs the radio terminal unit that the packets have beenbuffered by a traffic indication map (hereinafter referred to as “TIM”)included in a beacon.

As just described, a radio terminal unit operating in power-saving modereceives beacons intermittently from a radio base station. Afterreceiving each beacon, the radio terminal unit extracts informationelements. Having recognized from the TIM that the packets sent to theradio terminal unit itself had been buffered, the radio terminal unitsends the radio base station a control packet (hereinafter referred toas “PS-Poll”) requesting to deliver the buffered packets. Thus, theradio terminal unit receives its packets buffered by the radio basestation.

Additionally, a multicast/broadcast packet is sent to the radio terminalunit subsequent to a beacon with the DTIM. The radio terminal unitreceives at least a beacon with the DTIM in order to obtain themulticast/broadcast packet.

A power saving to the radio terminal unit can be achieved by lengtheningthe interval between the receiving of beacons from the radio basestation if there is no traffic. However, in the case where there arepackets for the radio terminal unit when the receiving interval has beenlengthened, the radio terminal unit can be late in obtaining the TIM,which causes delay in receiving the packets.

Besides, the radio base station buffers packets addressed to the radioterminal unit operating in power-saving mode in its memory.Consequently, when the receiving interval is lengthened on the radioterminal unit operating in power-saving mode, delivery of packets to theradio terminal unit is delayed. Thus, the radio base station has toretain the packets in the memory for a long period.

In the real-time communication of voice, moving images, etc., if theradio terminal unit which is in power-saving mode repeats transmissionand reception at long receiving intervals, packets addressed to theradio terminal unit are once buffered by the radio base station. Thebuffered packets are delivered to the radio terminal unit in the nextreceiving period, and, therefore, delay occurs in packet delivery.Especially, in the real-time communication of voice, moving images,etc., delay occurs in receiving packets on the radio terminal unit,which may cause a problem in the reproducibility of data.

In addition, the radio terminal unit in power-saving mode carries outthe intermittent receiving operation in timing with transmission ofbeacons each having the DTIM from the radio base station. That is, theradio terminal unit cannot determine the timing of the intermittentreceiving operation.

Moreover, in the case where a plurality of radio terminal units areconnected to the same radio base station and operate in power-savingmode, the respective radio terminal units have to perform theintermittent receiving operation based on the same intermittentreceiving timing, that is, the timing of transmission of beacons eachhaving the DTIM from the radio base station.

Further, the multicast/broadcast packet is sent to the radio terminalunit subsequent to a beacon with the DTIM. Therefore, the radio terminalunit, which operates in power-saving mode at long receiving intervalswithout reference to the beacon having the DTIM, may not be able toreceive the multicast/broadcast packet. For example, in the case where aphysical address resolution protocol message (ARP) is issued in anetwork for inquiring the physical address of the radio terminal unitoperating in power-saving mode, delay occurs in delivery to the radioterminal unit. As a result, the network is congested with the trafficcaused by retransmission.

Still further, in the wireless LAN communication, the CSMA/CA (CarrierSense Multiple Access protocol with Collision Avoidance) procedure isperformed in order to avoid a collision during data transmission.Regardless of communicating application, the same DIFS (DistributedInter Frame Space) is applied to every PS-Poll which the radio terminalunit transmits for requesting a radio base station to send packetsbuffered therein when the radio terminal unit is operating inpower-saving mode. Therefore, it is impossible to minimize delays and togive transmission right preferentially to real-time communication suchas voice communication.

Moreover, the back off algorithm is used when data are to betransmitted. That is, data are actually transmitted when random waittime has passed after the transmission right was given. Consequently, itis required to wait the random time regardless of the contents of senddata, which makes it impossible to minimize delays in real-timecommunication such as voice communication.

In order to solve the above-mentioned problems, the inventors haveproposed “a radio terminal and a radio communication system using thesame” in Japanese Patent Application No. 2002-291063. The radiocommunication system comprises a radio base station and radio terminalunits each being connected with a LAN or a WAN.

FIG. 1 is a timing chart illustrating the operation of the conventionalradio communication system for transmission and reception. In thefollowing, the operation of the radio communication system will beschematically described referring to FIG. 1.

Referring to FIG. 1, the radio terminal units 610, 620 and 630 belong toa radio base station 600. The radio base station 600 once bufferspackets to the radio terminal units that carry out the intermittentreceiving operation, and sends the packets to the respective radioterminal units on receipt of the PS-Poll (a control packet forrequesting a radio base station to deliver buffered packets).

The radio terminal units 610, 620 and 630 perform the intermittentreceiving operation at different intervals, respectively, in synchronismwith multiples of beacons transmitted by the radio base station 600 at aregular time interval. The intermittent receiving interval for each ofthe radio terminal units 610, 620 and 630 is determined according to theoperation mode of one or more communication applications running on eachterminal unit. In the example of FIG. 1, a “web browser” application isactive on the radio terminal unit 610, a “chat” application is active onthe radio terminal unit 620, and a “VoIP” (Voice over Internet Protocol)application is active on the radio terminal unit 630. The intermittentreceiving interval is selected from divisors of the interval between thetransmission of DTIM beacons (beacons each containing the DTIM) withinthe range of the beacon interval (an interval between the transmissionof respective beacons) to the DTIM beacon interval (an interval betweenthe transmission of respective DTIM beacons). In other words, theshortest intermittent receiving interval is the beacon interval, and thelongest is the DTIM beacon interval. Accordingly, each radio terminalunit can change the intermittent receiving interval depending on theoperation mode of the application running on it. Thereby power-savingcontrol on the radio terminal unit can be executed accurately.

Besides, the radio terminal units 610, 620 and 630 can maintain thepriorities of the PS-Polls transmitted to the radio base station 600.Such priorities are set based on the operation mode of the applicationrunning on the radio terminal units 610, 620 and 630. Consequently,packets of real-time communication such as voice packets can bepreferentially transmitted. Thus, it is possible to reduce delays andimprove voice quality.

With the conventional technique, each radio terminal unit transmits thePS-Poll to the radio base station triggered by the receipt of a beaconso as to receive packets addressed to it. In the case where a pluralityof radio terminal units are connected to one radio base station and acommunication application that is required to perform real-timeprocessing, such as a VoIP application, is running on the respectiveterminal units, the plural terminal units send the PS-Polls to the radiobase station, respectively, each time they receive beacons.Consequently, it is highly likely that the period of wait time from whenthe transmission right was given to data to when the data are actuallytransmitted is prolonged. As a result, delays are increased, whichaffects voice quality.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a radioterminal unit, a radio communication system and a communication controlmethod, more specifically, a radio terminal unit and a radiocommunication system, in which a radio base station connected to one ormore radio terminal units using radio as a transmission medium isconnected to a LAN (Local Area Network) or a WAN (Wide Area Network),capable of saving electric power of the radio terminal unit as well asimproving the quality of communication through a communicationapplication that requires real-time processing, that is, the quality ofreal-time communication such as voice communication.

It is another object of the present invention to provide a radioterminal unit and a radio communication system, capable of shorteningthe period of wait time before transmission which may be prolonged whena plurality of radio terminal units are connected to one radio basestation.

In accordance with an aspect of the present invention, to achieve theabove object, there is provided a radio terminal unit which runs inpower-saving mode and a radio base station a control packet forrequesting delivery so as to receive packets buffered by the radio basestation, comprising:

an operation mode of communication application determination unit fordetermining operation mode of one or more communication which isoperated at the radio terminal unit;

a control packet changing unit for changing a timing of transmission ofthe control packet according to the operation mode of one or morecommunication applications determined by the operation mode ofcommunication application determination unit; and

a communication control section for sending the control packet accordingto the timing of transmission changed by the control packet changingunit after the transmission of data from the application.

There may be provided the radio terminal unit according to the presentinvention as follows.

Preferably, a timing of transmission of the control packet is changed bythe control packet changing unit regardless of a beacon interval.

Preferably, the communication control section selects whether or not totransmit the control packet according to the operation mode of one ormore communication applications which are determined by the operationmode of communication application determination unit.

Preferably, the communication control section requests a power controlsection to turn on the power when the control packet is transmitted.

Preferably, the communication control section requests a power controlsection to turn off the power after the data reception by the controlpacket.

In accordance with another aspect of the present invention, there isprovided a radio communication system which is a radio network system,comprising one or more radio base stations and one or more radioterminal units runs in power-saving mode and a radio base station acontrol packet for requesting delivery so as to receive packets bufferedby the radio base station, comprising:

an operation mode of communication application determination unit fordetermining operation mode of one or more communication which isoperated at the radio terminal unit;

a control packet changing unit for changing a timing of transmission ofthe control packet according to the operation mode of one or morecommunication applications determined by the operation mode ofcommunication application determination unit; and

a communication control section for sending the control packet accordingto the timing of transmission changed by the control packet changingunit after the transmission of data from the application.

In accordance with an aspect of the present invention, to achieve theabove object, there is provided a communication control method of aradio terminal unit which runs in power-saving mode and a radio basestation a control packet for requesting delivery so as to receivepackets buffered by the radio base station, comprising an operation modeof communication application determination step of determining operationmode of one or more communication which is operated at the radioterminal unit and a communication control step of sending the controlpacket after the transmission data from the application according to thetiming of transmission of the control packet changed according to theoperation mode of one or more communication applications determined bythe operation mode of communication application determination step.

There may be provided the communication control method according to thepresent invention as follows.

Preferably, a timing of transmission of the control packet is changed bythe communication control step regardless of a beacon interval.

Preferably, the communication control step selects whether or not totransmit the control packet according to the operation mode of one ormore communication applications which are determined by the operationmode of communication application determination step.

Preferably, the communication control step requests a power controlsection to turn on the power when the control packet is transmitted.

Preferably, the communication control step requests a power controlsection to turn off the power after the data reception by the controlpacket.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a timing chart illustrating the operation of a conventionalradio communication system for transmission and reception;

FIG. 2 is a timing chart illustrating the operation of a radiocommunication system according to the first embodiment of the presentinvention;

FIG. 3 is a diagram showing the configuration of a radio network systemaccording to the first embodiment of the present invention;

FIG. 4 is a block diagram showing the configuration of a radio terminalunit according to the first embodiment of the present invention;

FIG. 5 is a flowchart for explaining part of the operation of acommunication control section of the radio terminal unit depicted inFIG. 4;

FIG. 6 is a flowchart for explaining part of the operation of acommunication control section according to the second embodiment of thepresent invention;

FIG. 7 is a flowchart for explaining part of the operation of acommunication control section according to the third embodiment of thepresent invention;

FIG. 8 is a flowchart for explaining the operation of the communicationcontrol section when there is a request for real-time processingaccording to the third embodiment of the present invention;

FIG. 9 is a block diagram showing the configuration of a radio terminalunit according to the fourth embodiment of the present invention;

FIG. 10 is a diagram showing examples of the contents of a communicatingapplication memory and a parameter memory depicted in FIG. 9;

FIG. 11 is a flowchart for explaining the operation of the radioterminal unit for determining whether real-time processing is necessaryor unnecessary based on communication applications according to thefourth embodiment of the present invention;

FIG. 12 is a block diagram showing the configuration of a radio terminalunit according to the sixth embodiment of the present invention;

FIG. 13 is a diagram showing an example of the contents of a parameterlimit memory depicted in FIG. 12; and

FIG. 14 is a flowchart for explaining part of the operation of the radioterminal unit according to the sixth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a timing chart illustrating the operation of a radiocommunication system according to the first embodiment of the presentinvention. In the following, the operation of the radio communicationsystem will be schematically described referring to FIG. 2.

In FIG. 2, the radio communication system includes a radio base station100 and radio terminal units 110 and 120. The radio terminal units 110and 120 belong to the radio base station 100. The radio base station 100once buffers packets addressed to the radio terminal units 110 and 120that carry out intermittent receiving operation, and sends the packetsto the respective radio terminal units 110 and 120 on receipt oftransmission requests from them.

The radio terminal units 110 and 120 are enabled for transmission andreception in synchronism with the timing of transmission of datagenerated by communication applications running on the respective radioterminal units 110 and 120. After transmitting the data, the radioterminal units 110 and 120 successively transmit the PS-Polls,respectively, to the radio base station 100 for requesting packets whichhave been buffered by the radio base station 100. When there arebuffered packets to the radio terminal units 110 and 120, the radio basestation 100 sends the packets to them. As for the timing of transmissionof data generated by a communication application running on the radioterminal unit, if the communication application requires real-timeprocessing and real-time communication is executed by employing, forexample, VoIP (Voice over Internet Protocol), packets are generated atregular intervals. When the communication application generates thepackets, for example, at intervals of 20 milli-seconds, the radioterminal unit transmits the PS-Polls at intervals of 20 milli-seconds.

In a conventional radio communication system, radio terminal units carryout the intermittent receiving operation based on beacons transmittedfrom a radio base station at regular intervals. Therefore, the beaconinterval (an interval between the transmission of respective beacons)has to be set at a minute value such as 20 milli-seconds. If the beaconinterval is lengthened and beacons are transmitted at intervals of, forexample, 200 milli-seconds, there is a high possibility that delayoccurs in the receipt of packets. However, in accordance with thepresent invention, it is possible to resolve such problems.

Besides, in a conventional radio communication system where each radioterminal unit transmits the PS-Poll to a radio base station insynchronism with the receipt of a beacon, a plurality of radio terminalunits may transmit the PS-Polls for requesting delivery of bufferedpackets to one radio base station all at once immediately after thereceipt of a beacon. Therefore, the radio terminal units are highlylikely to be placed in the transmission wait state. In other words, theperiod of wait time before transmission may be prolonged. However, inaccordance with the present invention, the radio terminal units 110 and120 transmit the PS-Polls to the radio base station 100, respectively,based on the timing of transmission of data therefrom. Thereby, thepossibility that the radio terminal units 110 and 120 are placed in thetransmission wait state is reduced. Thus, it is possible to cut downdelays and improve voice quality in real-time communication such asvoice communication.

Referring now to the drawings, a description of preferred embodiments ofthe present invention will be given in detail.

FIG. 3 is a diagram showing the configuration of a radio communicationsystem according to the first embodiment of the present invention.Referring to FIG. 3, the radio communication system comprises the radiobase station 100 connected to a LAN (Local Area Network) or a WAN (WideArea Network), the radio terminal units 110 and 120, and a terminal unit130 connected to a LAN or a WAN. The network system providescommunication of voice, moving images and the like.

After recognizing that each of the radio terminal units 110 and 120enters power-saving mode on receipt of a control packet therefrom, theradio base station 100 buffers packets to the terminal units 110 and 120in a memory within the base station 100, and informs the terminal units110 and 120 of the buffered packets by the TIM included in each beacon.

The radio terminal units 110 and 120 can communicate with the terminalunit 130 connected to a LAN or a WAN via the radio base station 100 bythe internet protocol (IP). The radio terminal units 110 and 120 conductconnection negotiations with the radio base station 100 using a wirelessphysical layer to thereby participate in the network. After thenegotiations are concluded, the radio terminal units 110 and 120 eachreceive a beacon from the radio base station 100, and extract respectiveinformation elements included in the beacon to obtain the beaconinterval. After that, radio terminal units 110 and 120 operate inintermittent receiving mode at DTIM beacon intervals, or intervalsbetween the transmission of respective DTIM beacons (beacons eachcontaining the DTIM).

FIG. 4 is a block diagram showing the configuration of the radioterminal unit according to the first embodiment of the presentinvention. Referring to FIG. 4, the radio terminal unit (110, 120)comprises a communication application section 300, an operation modedetermination section 310, a PS-Poll transmission timing memory 320, atimer control section 330, a power control section 340, a communicationcontrol section 350, and a radio communication interface section 360.

The communication application section 300 represents communicationapplications which are running on the radio terminal unit. While, inFIG. 4, the communication application section 300 indicates that n (n;an integer larger than 1) pieces of communication applications 30 _(i)to 30 _(n) are active, there may be no active application. When acommunication application is activated, the communication applicationsection 300 sets necessary parameters for the communication applicationin the operation mode determination section 310. In addition, thecommunication application section 300 informs the operation modedetermination section 310 as to the start and cutoff of communication.The communication application section 300 transmits/receives datathrough the communication control section 350.

The operation mode determination section 310 keeps activatedcommunication applications and parameters corresponding to therespective applications. Those values are set by the communicationapplication section 300. The operation mode determination section 310sets appropriate values in the PS-Poll transmission timing memory 320and the timer control section 330, respectively, based on the parametersof each application which is currently in communication set by thecommunication application section 300.

The PS-Poll transmission timing memory 320 stores the timing oftransmission of the PS-Poll corresponding to the active communicationapplications. The transmission timing is utilized by the communicationcontrol section 350. The operation mode determination section 310determines and sets this value in the PS-Poll transmission timing memory320.

The timer control section 330 operates when there is no activecommunication application that requires real-time processing. The timercontrol section 330 obtains the intermittent receiving interval from theoperation mode determination section 310, and continues to provide thepower control section 340 with a timer value at intervals correspondingto the obtained intermittent receiving interval. Additionally, the timercontrol section 330 have a function for correcting the timer valueaccording to the beacon receiving timing obtained from the communicationcontrol section 350. The communication control section 350 informs thetimer control section 330 as to a transition from a real-time processingunnecessary state (in which no communication application requiresreal-time processing) to a real-time processing necessary state (inwhich there is at least one communication application that requiresreal-time processing) and vice versa. In other words, the timing inwhich the timer control section 330 starts or stops operating as a timeris determined by the communication control section 350.

The power control section 340 repeatedly turns on or off the power ofthe radio communication interface section 360 in response to a poweron/off request from the communication control section 350. Besides, thepower control section 340 repeatedly turns on the power of the radiocommunication interface section 360 based on the timer value fed by thetimer control section 330, and turns off the power of the radiocommunication interface section 360 in response to the power off requestfrom the communication control section 350.

The communication control section 350 controls the radio communicationinterface section 360 to transmit data from the communicationapplication section 300 and to feed the section 300 with data receivedthrough the section 360. The communication control section 350 alsoconducts the negotiations with the radio base station 100. Havingreceived send data from the communication application section 300, thecommunication control section 350 sends the power on request to thepower control section 340 in order to turn on the power of the radiocommunication interface section 360. After all the data received fromthe communication application section 300 have been transmitted, thecommunication control section 350 determines whether or not to transmitthe PS-Poll to the radio base station 100 based on information from thePS-Poll transmission timing memory 320. When the communication controlsection 350 determines not to transmit the PS-Poll, the section 350sends the power off request to the power control section 340 in order toturn off the power of the radio communication interface section 360. Onthe other hand, when the communication control section 350 determines totransmit the PS-Poll, the section 350 transmits the PS-Polls to theradio base station 100 through the radio communication interface section360. Having received all packets corresponding to the transmittedPS-Polls, the communication control section 350 sends the power offrequest to the power control section 340. In addition, the communicationcontrol section 350 determines whether real-time processing is necessaryor unnecessary based on information from the PS-Poll transmission timingmemory 320. When the real-time processing necessary state changes to thereal-time processing unnecessary state, the communication controlsection 350 instructs the timer control section 330 to start operatingas a timer. In contrast, when the real-time processing unnecessary statechanges to the real-time processing necessary state, the communicationcontrol section 350 instructs the timer control section 330 to stopoperating as a timer.

The radio communication interface section 360 transmits data receivedfrom the communication control section 350 by radio. The radiocommunication interface section 360 also receives data sent by radiofrom the radio base station 100, and forwards the data to thecommunication control section 350. The power of the radio communicationinterface section 360 is turned on/off by the power control section 340.

In the following, a description will be given of the operation of theradio communication system according to the first embodiment of thepresent invention with reference to FIGS. 2 to 5.

Having been activated, the radio terminal unit (110, 120) conductsnegotiations with the radio base station 100. After the negotiations areconcluded, no communication application is in execution on the radioterminal unit (110, 120). At this point, since “real-time processingunnecessary” is set as the default in the PS-Poll transmission timingmemory 320, the radio terminal unit (110, 120) performs the ordinarypower-saving operation, that is, the intermittent receiving operation atDTIM beacon intervals.

When a communication application is activated, the communicationapplication section 300 informs the operation mode determination section310 of the AP-ID, a number that uniquely identifies the communicationapplication, and whether or not the communication application requiresreal-time processing (“real-time processing necessary” or “real-timeprocessing unnecessary”) as parameters. The AP-ID is uniquely assignedto each communication application.

After that, when the communication application actually enters intocommunication, the communication application section 300 informs theoperation mode determination section 310 as to the start ofcommunication. When informed as to a change in communication by thecommunication application section 300, the operation mode determinationsection 310 detects whether there is a communication application thatrequires real-time processing in all the communication applicationswhich are currently running on the radio terminal unit (110, 120).

When even only one communication application that requires real-timeprocessing has been detected, the operation mode determination section310 determines that the radio terminal unit (110, 120) is in thereal-time processing necessary state, and stores information, “real-timeprocessing necessary”, in the PS-Poll transmission timing memory 320. Onthe other hand, when there is no communication application that requiresreal-time processing, the operation mode determination section 310determines that the radio terminal unit (110, 120) is in the real-timeprocessing unnecessary state, and stores information, “real-timeprocessing unnecessary”, in the PS-Poll transmission timing memory 320.

The communication control section 350 instructs the timer controlsection 330 to start the timer when the real-time processing necessarystate changes to the real-time processing unnecessary state. Incontrast, the communication control section 350 instructs the timercontrol section 330 to stop the timer when the real-time processingunnecessary state changes to the real-time processing necessary state.When instructed to start timer control according to a transition to thereal-time processing unnecessary state, the timer control section 330provides the power control section 340 with a timer value based on thevalue which has been obtained from the operation mode determinationsection 310. Consequently, if the real-time processing necessary statechanges to the real-time processing unnecessary state due to the startof communication by the communication application, the intermittentreceiving interval of the radio terminal unit (110, 120) also changes.

Besides, when the established communication of a communicationapplication is cut off, the communication application section 300informs the operation mode determination section 310 as to the cutoff ofcommunication. Having received the information about the cutoff ofcommunication from the communication application section 300, theoperation mode determination section 310 determines that communicationhas been cut off, and deletes the informed AP-ID corresponding to thecommunication application from the AP-IDs of active communicationapplications. After that, the operation mode determination section 310checks whether real-time processing is necessary or unnecessary withrespect to each of all the communication applications which arecurrently running on the radio terminal unit (110, 120).

After that, the radio terminal unit (110, 120) operates in the manner aspreviously set forth. That is, when even only one communicationapplication that requires real-time processing has been detected, theoperation mode determination section 310 determines that the radioterminal unit (110, 120) is in the real-time processing necessary state,and stores information, “real-time processing necessary”, in the PS-Polltransmission timing memory 320. On the other hand, when there is nocommunication application that requires real-time processing, theoperation mode determination section 310 determines that the radioterminal unit (110, 120) is in the real-time processing unnecessarystate, and stores information, “real-time processing unnecessary”, inthe PS-Poll transmission timing memory 320.

In the case where the operation mode determination section 310 deletesall the AP-IDs of applications that have been in communication wheninformed on the cutoff of communication by the communication applicationsection 300, only AP-ID “0” given as a default value remains behind.Thereby, it is determined that real-time processing is unnecessary, and,therefore, the radio terminal unit (110, 120) carries out the ordinarypower-saving operation, that is, the intermittent receiving operation atDTIM beacon intervals in the same manner as when the negotiations withthe radio base station 100 have been concluded.

FIG. 5 is a flowchart for explaining the operation of the radio terminalunit (110, 120) for transmitting data to the terminal unit 130 connectedto a LAN or a WAN.

When the communication control section 350 receives send data addressedto the terminal unit 130 from the communication application section 300(step B1), the section 350 sends a power on request to the power controlsection 340 in order to turn on the power of the radio communicationinterface section 360. Having received the power on request to turn onthe power of the radio communication interface section 360, the powercontrol section 340 turns on the power of the radio communicationinterface section 360 (step B2). After the power control section 340turns on the power of the radio communication interface section 360, theradio communication interface section 360 is enabled for transmissionand reception of data. When the radio communication interface section360 has been enabled for transmission and reception of data, thecommunication control section 350 transmits the send data (step B3). Theradio base station 100 acknowledges the receipt of the data by returningan acknowledge signal (ACK) to the radio terminal unit (110, 120). Thetransmission of the data is completed on receipt of the acknowledgesignal (ACK).

Next, the communication control section 350 obtains information as towhether real-time processing is necessary or unnecessary stored in thePS-Poll transmission timing memory 320 (step B4).

When real-time processing is unnecessary (step B4, NO), thecommunication control section 350 sends a power off request to the powercontrol section 340 in order to turn off the power of the radiocommunication interface section 360 (step B8).

On the other hand, when real-time processing is necessary (step B4,YES), the communication control section 350 transmits the PS-Poll to theradio base station 100 (step B5). The radio terminal unit (110, 120)receives an acknowledge signal (ACK) from the radio base station 100 inresponse to the PS-Poll. Subsequently, when the radio base station 100has buffered packets to the radio terminal unit (110, 120), the terminalunit (110, 120) receives the buffered data (step B6). When the radiobase station 100 has not buffered packets to the radio terminal unit(110, 120), the terminal unit (110, 120) receives NULL data.

In the case where the radio terminal unit (110, 120) receives thepackets, the communication control section 350 determines whether or notbuffered packets to the radio terminal unit (110, 120) remain in theradio base station 100 based on information contained in the receiveddata (step B7). If buffered packets remain in the radio base station 100(step B7, YES), the communication control section 350 retransmits thePS-Poll to the radio base station 100 (return to step B5). When there isno buffered packet left and the radio terminal unit (110, 120) receivesNULL data (step B7, NO), the communication control section 350 sends apower off request to the power control section 340 in order to turn offthe power of the radio communication interface section 360 (step B8).

In the following, a concrete example of the operation of the radioterminal units 110 and 120 will be described in detail referring to FIG.2.

In FIG. 2, a “VoIP” application is active on each of the radio terminalunits 110 and 120. The radio terminal units 110 and 120 have alreadyconcluded negotiations with the radio base station 100, and the basestation 100 has been informed that the terminal units 110 and 120 areoperating in power-saving mode.

As can be seen in FIG. 2, the radio base station 100 transmits beaconsat regular intervals, and also transmits DTIM beacons at intervals ofcertain beacon intervals. After the negotiations, the radio base station100 once buffers packets addressed to the radio terminal units 110 and120 operating in power-saving mode in its memory. The radio base station100 sends the buffered packets to the radio terminal units 110 and 120upon receipt of transmission requests (PS-Poll) for requesting deliveryof buffered packets from the respective terminal units 110 and 120.

The active application on each of the radio terminal units 110 and 120requires real-time processing. It is assumed that the “VoIP” applicationthat requires real-time processing is running on the radio terminal unit110 and being in communication. When the communication applicationsection 300 has assigned AP-ID “1” for the “VoIP” application anddetermined that real-time processing is necessary for the application,the operation mode determination section 310 determines that the radioterminal unit 110 is in the real-time processing necessary state, andstores information, “real-time processing necessary”, in the PS-Polltransmission timing memory 320.

When send data is generated in the radio terminal unit 110, the power ofthe radio communication interface section 360 is turned on. Accordingly,the radio communication interface section 360 is enabled fortransmission and reception of data. Thus, the radio terminal unit 110transmits send data S1. Subsequently to the transmission of the senddata S1, the radio terminal unit 110 transmits the PS-Poll (PS1) to theradio base station 100 since the terminal unit 110 is in the real-timeprocessing necessary state. The radio base station 100 has received andbuffered packets addressed to the radio terminal unit 110. Therefore,the radio base station 100 transmits a buffered packet P1 to the radioterminal unit 110 on receipt of the PS-Poll (PS1). The radio terminalunit 110 receives the packet P1. If there is no buffered packet left inthe radio base station 100, the power of the radio communicationinterface section 360 is turned off, and the section 360 is disabled fortransmission and reception of data.

When send data is continuously generated in the radio terminal unit 110,the power of the radio communication interface section 360 is turned onas above described to transmit send data S3. Subsequently to thetransmission of the send data S3, the radio terminal unit 110 transmitsthe PS-Poll (PS3) to the radio base station 100 since the unit 110 is inthe real-time processing necessary state. Thereby, the radio terminalunit 110 receives the packet P3 buffered by the radio base station 100.After the radio terminal unit 110 has received all packets buffered bythe radio base station 100, the power of the radio communicationinterface section 360 is turned off in the manner as above described.

With regard to intervals between the generation of send data on theradio terminal unit 110, if the “VoIP” application which is running onthe units 110 packetizes data, for example, at sampling intervals of 20milli-seconds, send data are generated at intervals of 20 milli-seconds.Consequently, the radio terminal unit 110 carries out the intermittentreceiving operation (receipt of packets by sending the PS-Polls) atintervals of 20 milli-seconds. As just described, according to thepresent invention, the radio terminal unit 110 performs the intermittentreceiving operation independently of the beacon interval. Thus, it ispossible to reduce delay in receiving packets or data from the radiobase station 100.

On the other hand, when it has been determined that the radio terminalunit 110 is in the real-time processing unnecessary state, the power ofthe radio communication interface section 360 is turned off after thetransmission of send data without transmitting the PS-Poll to the radiobase station 100. The radio terminal unit 110 performs the intermittentreceiving operation at DTIM beacon intervals.

In FIG. 2, the radio terminal unit 120 operates in the same manner asthe radio terminal unit 110. If send data are generated in the radioterminal units 110 and 120 at similar intervals, it is hardly likelythat the timing of generation of send data S1 in the terminal unit 110is coincident with that of send data S2 in the terminal unit 120 sincethere is no dependency relation between the two as shown in FIG. 2.

In a conventional radio communication system, each radio terminal unittransmits the PS-Poll to a radio base station according to the receiptof a beacon. Consequently, it often happens that a plurality of radioterminal units transmit the PS-Polls to one radio base station all atonce immediately after the receipt of a beacon, thereby causingcollisions. However, according to the present invention, it is possibleto reduce the rate of collisions, which often take place in theconventional system because of traffic congestion after the receipt of abeacon. Thus, delays can be reduced. Additionally, even when send dataare generated in the plural radio terminal units at different intervals,respectively, it is also possible to reduce the rate of collisions whichoccur on the occasion of transmission. As a result, the effects ofdelays can be reduced.

While one communication application is active on the respective radioterminal units 110 and 120 in the first embodiment of the presentinvention, a plurality of communication applications may be runningconcurrently on the respective terminal units 110 and 120. In this case,the operation mode determination section 310 determines the operationmode of the radio terminal unit based on the operation mode of thecommunication applications, and the radio terminal unit operates orrequests for packet delivery based on the operation mode. Consequently,even when a plurality of radio terminal units are connected to the sameradio base station, the radio terminal units can perform theintermittent receiving operation differently from each other accordingto the operation mode of one or more communication applications whichare running on the respective terminal units.

In the following, a description will be made of the second embodiment ofthe present invention.

A radio terminal unit according to the second embodiment is in manyrespects basically similar to that of the first embodiment shown in FIG.4 except for the operation of the communication application section 300and the communication control section 350.

When a communication application is activated and send data isgenerated, the communication application section 300 sends the data tothe communication control section 350. At the same time, thecommunication application section 300 of the second embodiment providesthe communication control section 350 with information as to whetherreal-time processing is necessary or unnecessary as attached informationto the send data differently from that of the first embodiment. On thisoccasion, the communication application section 300 determines whetherreal-time processing is necessary or unnecessary. For example, when senddata is generated by a communication application that requires real-timeprocessing such as a VoIP application, the communication applicationsection 300 sends the data to the communication control section 350 withinformation, “real-time processing necessary”. On the other hand, whensend data is generated by a communication application that does notrequire real-time processing such as a web browser application, thecommunication application section 300 sends the data to thecommunication control section 350 with information “real-time processingunnecessary”.

The communication control section 350 operates essentially in the samemanner as that of the first embodiment except as set forth below. Thatis, in the first embodiment, the communication control section 350determines whether or not to transmit the PS-Poll with reference toinformation from the PS-Poll transmission timing memory 320 aftertransmitting send data received from the communication applicationsection 300. On the other hand, in the second embodiment, thecommunication control section 350 is provided with information as towhether or not to transmit the PS-Poll together with send data by thecommunication application section 300, and determines whether or not totransmit the PS-Poll based on the information after transmitting thesend data.

In the following, the operation of the radio terminal unit (110, 120)for transmitting data to the terminal unit 130 in the second embodimentwill be described in detail referring to FIG. 6. FIG. 6 is a flowchartfor explaining part of the operation of the communication controlsection 350 according to the second embodiment of the present invention.

When send data is generated, the communication application section 300feeds the communication control section 350 with information as towhether real-time processing is necessary or unnecessary in addition tothe send data (step F1). When the communication control section 350receives the send data addressed to the terminal unit 130 from thecommunication application section 300, the section 350 sends a power onrequest to the power control section 340 in order to turn on the powerof the radio communication interface section 360. Having received thepower on request to turn on the power of the radio communicationinterface section 360, the power control section 340 turns on the powerof the radio communication interface section 360 (step F2). After thepower control section 340 turns on the power of the radio communicationinterface section 360, the radio communication interface section 360 isenabled for transmission and reception of data. When the radiocommunication interface section 360 has been enabled for transmissionand reception of data, the communication control section 350 transmitsthe send data (step F3). The radio base station 100 acknowledges thereceipt of the data by returning an acknowledge signal (ACK) to theradio terminal unit (110, 120). The transmission of the data iscompleted on receipt of the acknowledge signal (ACK).

Next, the communication control section 350 determines whether real-timeprocessing is necessary or unnecessary based on the information as towhether real-time processing is necessary or unnecessary received fromthe communication application section 300 (step F4).

When real-time processing is unnecessary (step F4, NO), thecommunication control section 350 sends a power off request to the powercontrol section 340 in order to turn off the power of the radiocommunication interface section 360 (step F8).

On the other hand, when real-time processing is necessary (step F4,YES), the communication control section 350 transmits the PS-Poll to theradio base station 100 (step F5). The radio terminal unit (110, 120)receives an acknowledge signal (ACK) from the radio base station 100 inresponse to the PS-Poll. Subsequently, when the radio base station 100has buffered packets to the radio terminal unit (110, 120), the unit(110, 120) receives the buffered data (step F6). When the radio basestation 100 has not buffered packets to the radio terminal unit (110,120), the terminal unit (110, 120) receives NULL data.

In the case where the radio terminal unit (110, 120) receives thebuffered packets, the communication control section 350 determineswhether or not buffered packets to the radio terminal unit (110, 120)remain in the radio base station 100 based on information contained inthe received data (step F7). If buffered packets remain in the radiobase station 100 (step F7, YES), the communication control section 350retransmits the PS-Poll to the radio base station 100 (return to stepF5). When there is no buffered packet left and the radio terminal unit(110, 120) receives NULL data (step F7, NO), the communication controlsection 350 sends a power off request to the power control section 340in order to turn off the power of the radio communication interfacesection 360 (step F8).

As described above, the second embodiment of the present invention isdifferent from the first embodiment in that the communicationapplication section 300 provides the communication control section 350with information as to whether real-time processing is necessary orunnecessary as attached information to send data when sending the datato the section 350. More specifically, in the first embodiment, in thecase where communication applications, which differ from one another inthe necessity for real-time processing (e.g. a web browser applicationthat does not require real-time processing and a VoIP application thatrequires real-time processing), are concurrently running on the radioterminal unit and real-time processing is necessary, the communicationcontrol section transmits the PS-Poll after transmission of send datawithout identifying the communication application which has sent thedata to the communication control section. However, in accordance withthe second embodiment, the communication control section transmits thePS-Poll only after transmitting send data from a communicationapplication that requires real-time processing. Consequently,unnecessary transmission of the PS-Poll can be prevented, therebyenabling a more reduction in operating time. As a result, the radioterminal unit is usable for a longer period of time.

In the following, a description will be made of the third embodiment ofthe present invention.

A radio terminal unit according to the third embodiment is in manyrespects basically similar to that of the first embodiment shown in FIG.4 except for the operation of the operation mode determination section310 and the communication control section 350.

The operation mode determination section 310 of the third embodiment isinformed of a changeover in communication applications being incommunication by the communication application section 300, and informsthe communication control section 350 about the changeover differentlyfrom that of the first embodiment. In addition, the operation modedetermination section 310 keeps the intermittent receiving interval forthe occasion when real-time processing is required. The intermittentreceiving interval is utilized by the timer control section 330.

The communication control section 350 exercises control to transmit datafrom the communication application section 300 through the radiocommunication interface section 360, and to send data received throughthe radio communication interface section 360 to the communicationapplication section 300. On receipt of send data from the communicationapplication section 300, the communication control section 350 sends apower on request to the power control section 340 in order to turn onthe power of the radio communication interface section 360. Thecommunication control section 350 sends all data received from thecommunication application section 300. Those processes are performed asin the first embodiment.

However, in the third embodiment, the communication control section 350sends a power off request to the power control section 340 in order toturn off the power of the radio communication interface section 360after transmitting all send data. Having informed of a changeover inapplications being in communication by the operation mode determinationsection 310, the communication control section 350 obtains information,“real-time processing necessary” or “real-time processing unnecessary”from the PS-Poll transmission timing memory 320. The communicationcontrol section 350 performs the following processes based on theobtained information.

When there is no transition from the real-time processing necessary tounnecessary state and vice versa, the communication control section 350stays the same. Besides, when there is a transition from the real-timeprocessing unnecessary to necessary state, the communication controlsection 350 controls the timer control section 330 so as to provide thepower control section 340 with a timer value unrelated to the beaconinterval based on a value obtained from the operation mode determinationsection 310. On the other hand, when there is a transition from thereal-time processing necessary to unnecessary state, the communicationcontrol section 350 controls the timer control section 330 so as toprovide the power control section 340 with a timer value in synchronismwith the beacon interval based on a value obtained from the operationmode determination section 310.

In the following, the operation of the radio terminal unit in the thirdembodiment will be described in detail referring to FIG. 7. FIG. 7 is aflowchart for explaining part of the operation of the communicationcontrol section 350 according to the third embodiment of the presentinvention.

First, the operation mode determination section 310 is informed of achangeover in communication applications being in communication by thecommunication application section 300, and informs the communicationcontrol section 350 about the changeover in applications being incommunication (step D1).

Having informed of the changeover in applications being in communicationby the operation mode determination section 310, the communicationcontrol section 350 obtains information, “real-time processingnecessary” or “real-time processing unnecessary” from the PS-Polltransmission timing memory 320 (step D2). The communication controlsection 350 operates differently depending on the obtained information.

When there is no transition from the real-time processing necessary tounnecessary state and vice versa (step D3, YES), the communicationcontrol section 350 carries on current operation (step D9).

When there is a transition (step D3, NO) from the real-time processingunnecessary to necessary state (step D4, YES), the communication controlsection 350 instructs the timer control section 330 to provide thecommunication control section 350 with a timer value unrelated to thebeacon interval based on a value obtained from the operation modedetermination section 310 (step D5). After that, the communicationcontrol section 350 sends a power on request to the power controlsection 340 in synchronism with the timer value obtained from the timercontrol section 330 to turn on the power of the radio communicationinterface section 360 so that the radio communication interface section360 is enabled for transmission and reception of data. Thus, thecommunication control section 350 repeatedly transmits the PS-Poll tothe radio base station (step D6). The operation of the communicationcontrol section 350 in this instance is to be more fully describedhereinafter.

On the other hand, when there is a transition from the real-timeprocessing necessary to unnecessary state (step D4, NO), thecommunication control section 350 instructs the timer control section330 to provide the communication control section 350 with a timer valuein synchronism with the DTIM beacon interval based on a value obtainedfrom the operation mode determination section 310 (step D7). After that,the communication control section 350 sends a power on request to thepower control section 340 in synchronism with the timer value obtainedfrom the timer control section 330 to turn on the power of the radiocommunication interface section 360 so that the radio communicationinterface section 360 is enabled for transmission and reception of data.Thus, the communication control section 350 performs the intermittentreceiving operation based on the receipt of the DTIM beacon (step D8).

FIG. 8 is a flowchart for explaining the operation of the communicationcontrol section 350 when real-time processing is necessary according tothe third embodiment of the present invention.

When real-time processing is necessary, or when there is a transitionfrom the real-time processing unnecessary to necessary state, thecommunication control section 350 sends a power on request to the powercontrol section 340 based on the timer value obtained from the timercontrol section 330 to turn on the power of the radio communicationinterface section 360 so that the radio communication interface section360 is enabled for transmission and reception of data (step C1). Next,the communication control section 350 transmits the PS-Poll to the radiobase station (step C2). The radio terminal unit receives an acknowledgesignal (ACK) from the radio base station in response to the PS-Poll.Subsequently, when the radio base station has buffered packets to theradio terminal unit, the terminal unit receives the buffered data (stepC3). When the radio base station has not buffered packets to the radioterminal unit, the terminal unit receives NULL data.

In the case where the radio terminal unit receives the packets, thecommunication control section 350 determines whether or not bufferedpackets to the radio terminal unit remain in the radio base stationbased on information contained in the received data (step C4). Ifbuffered packets remain in the radio base station (step C4, YES), thecommunication control section 350 retransmits the PS-Poll to the radiobase station (return to step C2). When there is no buffered packet leftand the radio terminal unit receives NULL data (step C4, NO), thecommunication control section 350 sends a power off request to the powercontrol section 340 in order to turn off the power of the radiocommunication interface section 360 (step C5).

On the other hand, when real-time processing is unnecessary, or whenthere is a transition from the real-time processing necessary tounnecessary state, the communication control section 350 performs theintermittent receiving operation based on the DTIM beacon interval as inthe first embodiment.

As described above, in accordance with the third embodiment of thepresent invention, when real-time processing is necessary, the timing oftransmission of the PS-Poll is determined independently of both thetiming of transmission of send data and the beacon interval differentlyfrom the first embodiment. Namely, the PS-Poll is spontaneouslytransmitted from the radio terminal unit to the radio base station atintervals corresponding to communication applications. Therefore, evenin asymmetrical communication, such as broadcast, multicast andsimultaneous transmissive communication, that requires real-timeprocessing, it is possible to reduce the rate of collisions, which oftentake place when the timing of transmission of the PS-Poll is determinedbased on the beacon interval because a plurality of radio terminal unitstransmit the PS-Polls to one radio base station all at once immediatelyafter the receipt of a beacon. Thus, delay in receiving packets from theradio base station can be reduced, and the quality of communication canbe improved.

While, in the third embodiment, the operation mode determination section310 have the values for determining the timer value ready beforehand,the communication application section 300 may provide the operation modedetermination section 310 with the values.

Additionally, the third embodiment of the present invention may beapplicable in combination with the first and/or second embodiment.

In the following, a description will be made of the fourth embodiment ofthe present invention.

FIG. 9 is a block diagram showing the configuration of a radio terminalunit according to the fourth embodiment of the present invention. Theradio terminal unit shown in FIG. 9 is in many respects basicallysimilar to that of the first embodiment shown in FIG. 4 except for theconfiguration of the operation mode determination section 310, andsimilar numbers are utilized in designating corresponding portions ofthe unit. As can be seen in FIG. 9, the operation mode determinationsection 310 has more elaborate configuration as compared to that of thefirst embodiment.

The operation mode determination section 310 comprises a communicatingapplication memory 311, a parameter memory 312, a timer value memory313, an application communication management/control section 317, and aparameter determining section 318.

When a communication application is activated, the communicationapplication section 300 sets necessary parameters for the application inthe parameter memory 312. When a communication application isdeactivated, the communication application section 300 deletes theparameters set on startup for the application from the parameter memory312. In addition, the communication application section 300 informs theapplication communication management/control section 317 as to the startand cutoff of communication differently from the first embodiment.

The communicating application memory 311 stores applications currentlybeing in communication by values that uniquely identify them. Thosevalues are set by the application communication management/controlsection 317.

FIG. 10 is a diagram showing examples of the contents of thecommunicating application memory 311 and the parameter memory 312. InFIG. 10, for example, AP-ID “0” (401) is preset as a default value toindicate that no communication application is being executed, and storedin the communicating application memory 311. The communicatingapplication memory 311 keeps therein that applications with AP-ID “1”(402) and AP-ID “2” (404) are currently communicating.

The parameter memory 312 stores information as to whether real-timeprocessing is necessary or unnecessary with respect to each activecommunication application. The information, “real-time processingnecessary” or “real-time processing unnecessary” is set by thecommunication application section 300. As shown in FIG. 10, when theAP-ID is “0” (411), “real-time processing unnecessary” is set and storedin the parameter memory 312 beforehand.

Besides, the parameter memory 312 stores the power-saving ratecorresponding to each active communication application. The percentageis set by the communication application section 300. As shown in FIG.10, when the AP-ID is “0” (411), the power-saving rate is set at 100%,which is previously stored in the parameter memory 312. That is, in thecase where no application is active, the radio terminal unit of thefourth embodiment carries out the intermittent receiving operation atDTIM beacon intervals.

In addition, the parameter memory 312 stores a priority for each activecommunication application. The priority is set by the communicationapplication section 300. As shown in FIG. 10, when the AP-ID is “0”(411), “low” priority is set and stored in the parameter memory 312beforehand. In other words, when no application is active, the radioterminal unit of the fourth embodiment carries out the operation at thelevel of “low” priority.

The contents of the timer value memory 313 include a wake-up timer value314, an IFS (Inter Frame Space) timer value 315 and a random back offtime range 316. The wake-up timer value 314, the IFS (Inter Frame Space)timer value 315 and the random back off time range 316 are determinedand set by the parameter determining section 318. The parameterdetermining section 318 previously set the wake-up timer value 314 basedon the DTIM beacon interval obtained by receiving a beacon after thecompletion of negotiations with the radio base station. The IFS timervalue 315 and the random back off time range 316 stored in the timervalue memory 313 are used when the radio terminal unit actuallytransmits the PS-Poll or data to the radio base station. The parameterdetermining section 318 sets the IFS timer value 315 based on a DIFS(Distributed Inter Frame Space) value.

The application communication management/control section 317 is informedas to the AP-ID and the start and cutoff of communication by thecommunication application section 300. At the start of communication,the application communication management/control section 317 adds theAP-ID of an application has entered into communication into thecommunicating application memory 311. On the other hand, whencommunication is cut off, the application communicationmanagement/control section 317 deletes the AP-ID from the communicatingapplication memory 311. Additionally, the application communicationmanagement/control section 317 informs the parameter determining section318 about a changeover in communication applications being incommunication.

Having been informed about a changeover in communication applicationsbeing in communication by the application communicationmanagement/control section 317, the parameter determining section 318obtains the AP-IDs of applications currently being in communication fromthe communicating application memory 311 to recognize the applicationsbeing in communication. The parameter determining section 318 obtainsthe information as to whether real-time processing is necessary orunnecessary with respect to each communication application being incommunication from the parameter memory 312. When even only onecommunication application that requires real-time processing is present,the parameter determining section 318 stores information, “real-timeprocessing necessary”, in the PS-Poll transmission timing memory 320. Onthe other hand, when there is no communication application that requiresreal-time processing, the parameter determining section 318 storesinformation, “real-time processing unnecessary”, in the PS-Polltransmission timing memory 320.

Besides, the parameter determining section 318 obtains the power-savingrates for applications being in communication from the parameter memory312. Subsequently, the parameter determining section 318 finds out theintermittent receiving interval for the radio terminal unit according tothe lowest power-saving rate of the obtained power-saving rates usingthe DTIM beacon interval and the beacon interval (TIM beacon interval)fed by the communication control section 350. After that, the parameterdetermining section 318 sets the intermittent receiving interval as thewake-up timer value 314 in the timer value memory 313.

At the same time, the parameter determining section 318 obtains thepriorities for applications being in communication from the parametermemory 312, and finds out the highest priority of the obtainedpriorities. Based on the highest priority, the parameter determiningsection 318 determines the IFS timer value 315 and the random back offtime range 316 used when the radio terminal unit actually transmits thePS-Poll or data to the radio base station. The parameter determiningsection 318 sets the IFS timer value 315 and the random back off timerange 316 in the timer value memory 313.

The PS-Poll transmission timing memory 320 stores the timing oftransmission of the PS-Poll corresponding to the active communicationapplications. The transmission timing is utilized by the communicationcontrol section 350. The parameter determining section 318 determinesand sets this value in the PS-Poll transmission timing memory 320.

The timer control section 330 operates when there is no activecommunication application that requires real-time processing in thecommunication application section 300. The timer control section 330obtains the intermittent receiving interval from the wake-up timer value314, and continues to provide the power control section 340 with a timervalue at intervals (at intervals of one or more beacon intervals)corresponding to the wake-up timer value 314. The timer control section330 starts providing the timer value on the basis of the receipt of abeacon with the DTIM. Additionally, the timer control section 330corrects the timer value according to the beacon receiving timingobtained from the communication control section 350. The communicationcontrol section 350 informs the timer control section 330 as to atransition from real-time processing unnecessary to necessary state andvice versa. That is, the timer control section 330 starts or stopsoperating as a timer under the control of the communication controlsection 350.

In the following, a description will be given of the operation of theradio communication system according to the fourth embodiment of thepresent invention with reference to FIGS. 9 to 11.

Having been activated, the radio terminal unit (110, 120) conductsnegotiations with the radio base station 100. After the negotiations areconcluded, no communication application is in execution on the radioterminal unit (110, 120). At this point, since “real-time processingunnecessary” is set as the default in the PS-Poll transmission timingmemory 320, the radio terminal unit (110, 120) performs the ordinarypower-saving operation, that is, the intermittent receiving operation atDTIM beacon intervals.

FIG. 11 is a flowchart for explaining the operation of the radioterminal unit (110, 120) for determining whether real-time processing isnecessary or unnecessary based on communication applications inexecution on the terminal unit (110, 120).

When a communication application is activated, the communicationapplication section 300 stores the AP-ID of the application and theinformation as to whether or not the application requires real-timeprocessing in the parameter memory 312. The AP-ID is uniquely assignedto each communication application. For example, AP-ID “1” is assigned tothe activated communication application. At the same time, thepower-saving rate and priority for the communication application isstored in the parameter memory 312. In the example of FIG. 10, suchinformation as “real-time processing necessary”, a power-saving rate of“10%” and “low priority” is stored in relation to AP-ID “1” (412) in theparameter memory 312.

After that, when the communication application actually enters intocommunication in the communication application section 300, theapplication communication management/control section 317 is informed asto the start of communication. More specifically, the applicationcommunication management/control section 317 is informed that, forexample, the communication application with AP-ID “1” has entered intocommunication.

When informed as to the start of communication by the communicationapplication section 300, the application communicationmanagement/control section 317 determines that communication has beenstarted (FIG. 11, step A1, START), and, as shown in FIG. 10, adds theinformed AP-ID, for example, AP-ID “1” (402) into the communicatingapplication memory 311 (step A2). Having added the AP-ID into thecommunicating application memory 311, the application communicationmanagement/control section 317 informs the parameter determining section318 that a changeover has been made in communication.

When receiving the information about the changeover in communicationfrom the application communication management/control section 317, theparameter determining section 318 searches the communicating applicationmemory 311 for applications currently being in communication, andobtains the AP-IDs of the applications (step A3). Next, the parameterdetermining section 318 searches the parameter memory 312 to obtaininformation as to whether real-time processing is necessary orunnecessary corresponding to the respective AP-IDs of all thecommunication applications (step A4). In the example of FIG. 10, if theobtained AP-IDs of the applications being in communication are “0”(411), “1” (412) and “3” (414), the obtained information for therespective AP-IDs “0”, “1” and “3” is “real-time processingunnecessary”, “real-time processing necessary” and “real-time processingunnecessary”.

When even only one communication application that requires real-timeprocessing is present, the parameter determining section 318 determinesthat the radio terminal unit (110, 120) is in the real-time processingnecessary state (step A5), and stores information, “real-time processingnecessary”, in the PS-Poll transmission timing memory 320 (step A6). Inthe above case, the parameter determining section 318 determines thatthe radio terminal unit (110, 120) is in the real-time processingnecessary state, and stores information, “real-time processingnecessary”, in the PS-Poll transmission timing memory 320 sinceinformation, “real-time processing unnecessary”, “real-time processingnecessary” and “real-time processing unnecessary”, has been obtained forthe respective AP-IDs “0”, “1” and “3”.

When receiving the information about the changeover in communicationfrom the application communication management/control section 317, theparameter determining section 318 searches the communicating applicationmemory 311 for applications currently being in communication, andobtains the AP-IDs of the applications as described previously. Afterthat, the parameter determining section 318 also obtains power-savingrates in relation to the respective AP-IDs of all the communicationapplications from the parameter memory 312. In the example of FIG. 10,if the obtained AP-IDs of the applications being in communication are“0” (411), “1” (412) and “3” (414), power-saving rates “100%”, “10%” and“100%” are obtained for the AP-IDs “0”, “1” and “3”, respectively.

Subsequently, the parameter determining section 318 selects the lowestpower-saving rate from the obtained power-saving rates. Then, theparameter determining section 318 finds out the intermittent receivinginterval based on the lowest power-saving rate. One approach to findingout the intermittent receiving interval involves following processes.First, the parameter determining section 318 finds out divisors of theDTIM interval. Then, the parameter determining section 318 divides thepercentage (100%) equally by the number of the divisors, and uses adivisor corresponding to the lowest power-saving rate as theintermittent receiving interval. For example, if the DTIM interval is“8”, there are four divisors, “1”, “2”, “4” and “8”. Therefore, whendivided equally among the divisors “1”, “2”, “4” and “8”, the percentage(100%) is divided into four parts, that is, from 0% to 25% for “1”, from26% to 50% for “2”, from 51% to 75% for “4” and from 76% to 100% for“8”. In the above case, the parameter determining section 318 decides on“1” as the intermittent receiving interval since the lowest power-savingrate of the obtained power-saving rates is 10%. Thus, the parameterdetermining section 318 determines the intermittent receiving interval,and stores the determined value in the timer value memory 313 as thewake-up timer value 314.

The communication control section 350 instructs the timer controlsection 330 to start the timer when the real-time processing necessarystate changes to the real-time processing unnecessary state. Incontrast, the communication control section 350 instructs the timercontrol section 330 to stop the timer when the real-time processingunnecessary state changes to the real-time processing necessary state.When instructed to start timer control according to a transition to thereal-time processing unnecessary state, the timer control section 330continuously multiplies the beacon interval based on the wake-up timervalue 314 stored in the timer value memory 313, and provides the powercontrol section 340 with a timer value on the basis of the product.Consequently, when the wake-up timer value 314 changes due to the startof communication by a communication application, the intermittentreceiving interval for the radio terminal unit (110, 120) in thereal-time processing unnecessary state also changes.

When receiving the information about the changeover in communicationfrom the application communication management/control section 317, theparameter determining section 318 searches the communicating applicationmemory 311 for applications currently being in communication, andobtains the AP-IDs of the applications as described previously. Afterthat, the parameter determining section 318 also obtains priorities inrelation to the respective AP-IDs of all the communication applicationsfrom the parameter memory 312. In the example of FIG. 10, if theobtained AP-IDs of the applications being in communication are “0”(411), “1” (412) and “3” (414), “low”, “high” and “middle” prioritiesare obtained for the AP-IDs “0,”, “1” and “3”, respectively.

Subsequently, the parameter determining section 318 selects the highestpriority from the obtained priorities. Then, the parameter determiningsection 318 determines the IFS timer value and the range of random backoff time based on the highest priority. The IFS timer value and therandom back off time range may be determined in the following manner.The parameter determining section 318 sets the IFS timer value using theDIFS. For example, in the case of “high” priority, the parameterdetermining section 318 sets the IFS timer value to DIFS-2t. In the caseof “middle” priority, the IFS timer value is set to DIFS-t. In the caseof “low” priority, the IFS timer value is set to DIFS (t: arbitrarilyvalue).

Besides, assuming that the maximum value of normal random back off timeis R, the parameter determining section 318 sets the random back offtime range, for example, to 0 to 0.5 R in the case of “high” priority.In the case of “middle” priority, the random back off time range is setto 0 to 0.75 R. In the case of “low” priority, the random back off timerange is set to 0 to R. In the above case, the parameter determiningsection 318 determines that the IFS timer value is “DIFS-2t”, and thatthe random back off time range is the narrowest range of “0 to 0.5 R”since the highest priority of the obtained priorities is “high”priority. Thus, the parameter determining section 318 determines the IFStimer value and the range of random back off time, and stores thedetermined values in the timer value memory 313 as the IFS timer value315 and the random back off time range 316.

When required by the communication control section 350, the timercontrol section 330 continuously provides the power control section 340with a timer value on the basis of the IFS timer value 315 and therandom back off time range 316. Consequently, when the IFS timer value315 and the random back off time range 316 change due to the start ofcommunication by a communication application, the timer value used whenthe radio terminal unit (110, 120) transmits data or the PS-Poll alsochange.

On the other hand, when the established communication of a communicationapplication is cut off, the communication application section 300informs the application communication management/control section 317 asto the cutoff of communication. Having received the information aboutthe cutoff of communication from the communication application section300, the application communication management/control section 317determines that communication has been cut off (step A1, CUTOFF), anddeletes the AP-ID corresponding to the informed communicationapplication from the communicating application memory 311 (step A7).

After deleting the corresponding AP-ID from the communicatingapplication memory 311, the application communication management/controlsection 317 informs the parameter determining section 318 that achangeover has been made in communication. After that, the operationproceeds to step A3, and the aforementioned processes are performed.

In the case where the application communication management/controlsection 317 deletes all the AP-IDs of applications that have been incommunication from the communicating application memory 311 at step A7,only AP-ID “0” given as a default value remains behind. Thereby, it isdetermined that real-time processing is unnecessary since there is noapplication being in communication. Consequently, the radio terminalunit (110, 120) performs the ordinary power-saving operation, that is,the intermittent receiving operation at DTIM beacon intervals. Besides,the communication control section 350 carries out the transmittingoperation using the normal DIFS value and random back off time range.

In the fourth embodiment, the radio terminal unit (110, 120) transmitsdata to another terminal unit 130 in the same manner as the radioterminal unit (110, 120) of the first embodiment described previously inconnection with FIG. 5.

As is described above, according to the fourth embodiment of the presentinvention, the timer value memory 313 stores the IFS timer value 315 andthe random back off time range 316 used when transmitting data or thePS-Poll. Consequently, priorities can be set according to applicationsbeing in communication. Thus, in real-time communication such as voicecommunication, the effects of delays can be reduced.

In the following, a description will be made of the fifth embodiment ofthe present invention.

The radio terminal unit of the fifth embodiment is of the sameconfiguration as that of the fourth embodiment shown in FIG. 9, however,operates differently as in the case of the first and third embodiments.That is, the fifth embodiment differs from the fourth embodiment in theoperation of the parameter determining section 318, the timer controlsection 330 and the communication control section 350.

The parameter determining section 318 of the fifth embodiment isdifferent from that of the fourth embodiment in that, when informed of achangeover in communication applications being in communication by theapplication communication management/control section 317, the parameterdetermining section 318 informs the communication control section 350about the changeover.

Besides, the timer control section 330 of the fifth embodiment isdifferent from that of the fourth embodiment in that the section 330provides the communication control section 350 with a timer valuesynchronized with the beacon interval or a timer value unrelated to thebeacon interval based on the wake-up timer value 314 by request from thecommunication control section 350. In other words, the timer controlsection 330 makes a switch between the two values by request from thecommunication control section 350.

The communication control section 350 exercises control to transmit datafrom the communication application section 300 through the radiocommunication interface section 360, and to send data received throughthe radio communication interface section 360 to the communicationapplication section 300. In addition, the communication control section350 conducts the negotiations with the radio base station 100. Onreceipt of send data from the communication application section 300, thecommunication control section 350 sends a power on request to the powercontrol section 340 in order to turn on the power of the radiocommunication interface section 360. The communication control section350 sends all data received from the communication application section300. Those processes are performed as in the fourth embodiment.

However, in the fifth embodiment, the communication control section 350sends a power off request to the power control section 340 in order toturn off the power of the radio communication interface section 360after transmitting all send data. Having informed of a changeover inapplications being in communication by the parameter determining section318, the communication control section 350 obtains information,“real-time processing necessary” or “real-time processing unnecessary”from the PS-Poll transmission timing memory 320.

When there is a transition from the real-time processing unnecessary tonecessary state, the communication control section 350 controls thetimer control section 330 so as to provide the power control section 340with a timer value unrelated to the beacon interval based on the wake-uptimer value 314. On the other hand, when there is a transition from thereal-time processing necessary to unnecessary state, the communicationcontrol section 350 controls the timer control section 330 so as toprovide the power control section 340 with a timer value in synchronismwith the beacon interval based on the wake-up timer value 314. That is,the communication control section 350 of the fifth embodiment operatesin the same manner as that of the third embodiment.

In the following, a description will be given of the operation of theradio terminal unit according to the fifth embodiment of the presentinvention. The fifth embodiment is basically similar to the fourthembodiment except for the operation of the parameter determining section318, the timer control section 330 and the communication control section350.

The parameter determining section 318 determines information to bestored in the PS-Poll transmission timing memory 320 and respectivevalues to be stored in the timer value memory 313 in the same manner asdescribed previously for the fourth embodiment. As mentioned above, inthis embodiment, the communication control section 350 operatessimilarly to that of the third embodiment.

According to the fifth embodiment of the present invention, the timervalue memory 313 stores the IFS timer value 315 and the random back offtime range 316 used when transmitting data or the PS-Poll as in thefourth embodiment. Consequently, priorities can be set according toapplications being in communication. Thus, in real-time communicationsuch as voice communication, the effects of delays can be reduced.

As described above, in accordance with the fifth embodiment of thepresent invention, when real-time processing is required, the timing oftransmission of the PS-Poll is determined independently of both thetiming of transmission of send data and the beacon interval differentlyfrom the fourth embodiment. Namely, the PS-Poll is spontaneouslytransmitted from the radio terminal unit to the radio base station atintervals corresponding to communication applications. Therefore, evenin asymmetrical communication, such as broadcast, multicast andsimultaneous transmissive communication, that requires real-timeprocessing, it is possible to reduce the rate of collisions, which oftentake place when the timing of transmission of the PS-Poll is determinedbased on the beacon interval because a plurality of radio terminal unitstransmit the PS-Polls to one radio base station all at once immediatelyafter the receipt of a beacon. Thus, delay in receiving packets from theradio base station can be reduced, and the quality of communication canbe improved.

Additionally, the fifth embodiment of the present invention may beapplicable in combination with the first, second and/or fourthembodiment.

In the following, a description will be made of the sixth embodiment ofthe present invention.

FIG. 12 is a block diagram showing the configuration of a radio terminalunit according to the sixth embodiment of the present invention. Theradio terminal unit shown in FIG. 12 is in many respects basicallysimilar to that of the fourth embodiment shown in FIG. 9 except for thepresence of a battery charge detector 500 and a parameter limit memory510, and similar numbers are utilized in designating correspondingportions of the terminal unit. Further, the operation mode determinationsection 310 operates differently from those of the first to thirdembodiments shown in FIG. 4, and the parameter determining section 318operates differently from those of the fourth and fifth embodimentsshown in FIG. 9.

Upon receipt of a request to detect the remaining battery charge fromthe parameter determining section 318, the battery charge detector 500measures the remaining amount of battery charge. Then, the batterycharge detector 500 informs the parameter determining section 318 of theremaining amount.

FIG. 13 is a diagram showing an example of the contents of the parameterlimit memory 510. As can be seen in FIG. 13, the parameter limit memory510 stores limits 521 and 531 on the power-saving rate and limits 522and 532 on the priority of communication set for the ranges ofproportions of remaining battery charge 520 and 530. These limits arestored in the parameter limit memory 510 in advance.

The parameter determining section 318 reads the limits out of theparameter limit memory 510. The parameter determining section 318 setsthe respective values stored in the timer value memory 313 withreference to the limits which have been set with respect to each rangeof proportions of remaining battery charge differently from theaforementioned operation mode determination section 310 or parameterdetermining section 318 in the first to fifth embodiments.

In the following, a description will be given of the operation of theradio terminal unit according to the sixth embodiment of the presentinvention with reference to FIGS. 13 and 14. The sixth embodiment is inmany respects basically similar to the above-mentioned embodiments, and,therefore, only the operation of the parameter determining section 318will be described.

FIG. 14 is a flowchart for explaining part of the operation of theparameter determining section 318 according to the sixth embodiment ofthe present invention. As in the above-mentioned fourth and fifthembodiments, the parameter determining section 318 searches thecommunicating application memory 311 for applications currently being incommunication (step E51). Next, the parameter determining section 318searches the parameter memory 312 to obtain information, such aspower-saving rate and priority corresponding to all the communicationapplications, and select specific information, for example, the lowestpower-saving rate and the highest priority (step E52), and determinesthe respective values to be stored in the timer value memory 313according to the selected information (step E53).

After that, in the sixth embodiment, the parameter determining section318 obtains the proportion of remaining battery charge from the batterycharge detector 500 (step E54). Subsequently, the parameter determiningsection 318 obtains limits from the parameter limit memory 510 based onthe proportion of remaining battery charge to set the respective valuesin the timer value memory 313 (step E55). Then, the parameterdetermining section 318 compares the information selected at step E52with the limits obtained at step E55 (step E56).

Based on the result of the comparison at step E56, the parameterdetermining section 318 determines whether to use the informationselected at step E52 or the limits obtained at step E55. A choicebetween the two is made depending on the comparison result.

For example, in the case of determining the power-saving rate, theparameter determining section 318 compares the power-saving rateselected at step E52 with the limit on the power-saving rate obtained atstep E55. If the power-saving rate selected at step E52 is equal to orhigher than the limit, the parameter determining section 318 determinesto use the power-saving rate selected at step E52 (step E57, NO).Consequently, the respective values in the timer value memory 313determined at step E53 remain the same (step E58). On the other hand,when the power-saving rate selected at step E52 is lower than the limit,the limit is to be used (step E57, YES). That is, the parameterdetermining section 318 resets the respective values in the timer valuememory 313 according to the limit (step E61).

In the case of determining the priority, if the priority selected atstep E52 is equal to or higher than the limit on priority obtained atstep E55, the parameter determining section 318 determines to use thepriority selected at step E52 (step E57, NO). On the other hand, whenthe priority selected at step E52 is lower than the limit, the limit isto be used (step E57, YES).

Thereby, when the remaining amount of battery charge has reduced to lessthan a certain value, the radio terminal unit does not carry out theintermittent receiving operation at an interval shorter than theintermittent receiving interval which has been determined based on thelimits set in the parameter limit memory 510. In addition, anapplication can be terminated normally by increasing the priority ofcommunication.

In accordance with the sixth embodiment of the present invention, theradio terminal unit includes the battery charge detector 500 and theparameter limit memory 510. With this construction, it becomes possibleto adjust or reset the power-saving rate when remaining battery chargehas reduced so that the radio terminal unit can be used as long aspossible. Moreover, an application can be terminated normally beforeabruptly interrupted during communication.

Incidentally, the battery charge detector 500 may regularly checkremaining battery charge. In this case, when the battery charge detector500 detects that the proportion of remaining battery charge has changedand come to fall in another range of proportions of remaining batterycharge with reference to the parameter limit memory 510, the detector500 informs the parameter determining section 318 about this. On receiptof the information from the battery charge detector 500, the parameterdetermining section 318 updates the respective values stored in thetimer value memory 313 if necessary. Thereby, it is possible to respondto a change in remaining battery charge during communication.

Additionally, the sixth embodiment of the present invention may beapplicable in combination with the third, fourth and/or fifthembodiment.

While a description has been made of communication between the radioterminal unit (110, 120) and the terminal unit 130 that is connected toa LAN or a WAN, the radio terminal unit 110 can communicate with theradio terminal unit 120 connected to the same radio base station 100 ina similar manner.

Besides, when real-time processing is required, the radio terminal unitmay conduct the intermittent receiving operation at DTIM beaconintervals together with the intermittent receiving operation accordingto the present invention. By this means, the radio terminal unit doesnot miss receiving a multicast/broadcast packet.

In the above-described embodiments, a “VoIP” application is taken as anexample of the communication application which is running on the radioterminal unit. However, the radio terminal unit of the present inventionoperates in a similar manner with any other communication applicationsuch as “television-phone”, “chat”, “web browser” and “instant message”.

In the above-described embodiments, the communication applicationsection 300 sets necessary parameters for respective communicationapplications in the operation mode determination section 310. However,the parameters may be set in the operation mode determination section310 beforehand. In addition, the parameters may be automatically changedaccording to the contents of communicated data.

As set forth hereinabove, in accordance with the present invention, thetiming of transmission of the control packet can be changed according tothe operation mode of one or more communication at the radio terminalunit side irrespective of the beacon interval. Consequently, even whenthere is any application being in communication on the radio terminalunit, electric power consumption by the terminal unit can be reduced asmuch as possible. As a result, available time of the radio terminal unitcan be prolonged.

In a conventional radio communication system, each radio terminal unitsends a radio base station the PS-Poll for receiving packets buffered inthe radio base station based on the receipt of a beacon. Therefore, whena plurality of radio terminal units are connected to one radio basestation and communication applications that require real-timeprocessing, such as a “VoIP” application, are running on them, it oftenhappens that the radio terminal units transmit the PS-Polls to the radiobase station all at once immediately after the receipt of a beacon,thereby causing collisions.

However, according to the present invention, when real-time processingis required, the radio terminal units transmit the PS-Polls to the radiobase station based on the timing of generation of send data therein.Thereby, it is possible to reduce the rate of collisions, which oftentake place in the conventional system due to traffic congestion afterthe transmission of a beacon. Thus, waiting time on the occasion of datatransmission can be reduced. Thus, it is possible to prevent thedeterioration of voice quality in real-time communication such as voicecommunication.

Moreover, the radio terminal unit that performs the intermittentreceiving operation can freely change the intermittent receivinginterval by the setting on the radio terminal unit side only regardlessof the radio base station. That is, each radio terminal unit can changeits intermittent receiving interval without being affected by otherradio terminal units connected to the same radio base station. Thus, inthe case where a plurality of radio terminal units are connected to oneradio base station, the respective radio terminal units can perform theintermittent receiving operation at their individual intermittentreceiving intervals.

Further, there is no need for any special radio base station since theradio terminal unit that performs the intermittent receiving operationcan freely change the intermittent receiving interval by the setting onthe radio terminal unit side only regardless of the radio base station.Consequently, many existing radio base stations are readily available.

Still further, in most cases, the radio terminal unit that performs theintermittent receiving operation of the present invention transmits thePS-Poll to the radio base station before receiving a beacon.Consequently, the radio terminal unit can receive its packets earlier ascompared to the radio terminal unit that operates in an ordinaryintermittent receiving mode in synchronism with DTIM beacons.Accordingly, delays in packet delivery can be reduced. Thus, it ispossible to improve voice quality in real-time communication such asvoice communication.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentwithout departing from the scope and spirit of the present invention.

1. A radio terminal unit which runs in power-saving mode and sends aradio base station a control packet for requesting delivery so as toreceive packets buffered by the radio base station, comprising: anoperation mode of communication application determination unit fordetermining operation mode of one or more communication which isoperated at the radio terminal unit; a control packet changing unit forchanging a timing of transmission of the control packet according to theoperation mode of one or more communication applications determined bythe operation mode of communication application determination unit; anda communication control section for sending the control packet accordingto the timing of transmission changed by the control packet changingunit after the transmission of data from the application.
 2. The radioterminal unit claimed in claim 1, wherein the timing of transmission ofthe control packet is changed by the control packet changing unitregardless of a beacon interval.
 3. The radio terminal unit claimed inclaim 1, wherein the communication control section selects whether ornot to transmit the control packet according to the operation mode ofone or more communication applications which are determined by theoperation mode of communication application determination unit.
 4. Theradio terminal unit claimed in claim 3, wherein the communicationcontrol section requests a power control section to turn on the powerwhen the control packet is transmitted.
 5. The radio terminal unitclaimed in claim 1, wherein the communication control section requests apower control section to turn off the power after the data reception bythe control packet.
 6. A radio communication system which is a radionetwork system, comprising: one or more radio base stations; and one ormore radio terminal units which runs in power-saving mode and a radiobase station a control packet for requesting delivery so as to receivepackets buffered by the radio base station, comprising: an operationmode of communication application determination unit for determiningoperation mode of one or more communication which is operated at theradio terminal unit; a control packet changing unit for changing atiming of transmission of the control packet according to the operationmode of one or more communication applications determined by theoperation mode of communication application determination unit; and acommunication control section for sending the control packet accordingto the timing of transmission changed by the control packet changingunit after the transmission of data from the application.
 7. Acommunication control method of a radio terminal unit which runs inpower-saving mode and a radio base station a control packet forrequesting delivery so as to receive packets buffered by the radio basestation, comprising an operation mode of communication applicationdetermination step of determining operation mode of one or morecommunication which is operated at the radio terminal unit and acommunication control step of sending the control packet after thetransmission data from the application according to the timing oftransmission of the control packet changed according to the operationmode of one or more communication applications determined by theoperation mode of communication application determination step.
 8. Acommunication control method claimed in claim 7, wherein the timing oftransmission of the control packet is changed by the communicationcontrol step regardless of a beacon interval.
 9. A communication controlmethod claimed in claim 7, wherein the communication control stepselects whether or not to transmit the control packet according to theoperation mode of one or more communication applications which aredetermined by the operation mode of communication applicationdetermination step.
 10. A communication control method claimed in claim9, wherein the communication control step requests a power controlsection to turn on the power when the control packet is transmitted. 11.A communication control method claimed in claim 7, wherein thecommunication control step requests a power control section to turn offthe power after the data reception by the control packet.